> 
> *Hmm... Time to take inventory of the slimes real quick... Lamp Oil Slime, O- Slime, Yellow Paint Slime, Pur-... **Red Paint Slime? Blue Paint Slime?** You two didn't...! Great... So I need a new RPS and a new BPS. That's going to be annoying to make. Note to self, ask some adventurers to grab me two new slimes from the wild.*
> 
> 
> *Let's check the Food Slimes now... Honey Slime? Check. Grape Jelly Slime? Check. Chocolate Slime? Oh, you split and made a second one... Awesome! Hey, little guy, you're about to make me some serious money! Maple Syrup Slime? Check. Butter Slime? Check. Barbecue Slime...? Barbecue Slime...?! Ugh, not another one... Add **that** to the number of slimes I need to remake... That's really going to hurt the wallet since we're out of brown sugar... Maybe I can get an adventurer to help figure out how I can keep the slimes from mixing and escaping?*
> 
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> 

Well, adventurers? This is a formal Quest being put out to the entirety of the WB.SE Adventurer's Guild. In the past month, I've lost over a dozen slimes. Either they have eaten each other, mixed with each other, or escaped their enclosures/pens altogether and have either run off or been stolen. How can I prevent the loss of any more slimes? I use them for various purposes including selling what they produce, much like a beekeeper.

Info about the slimes:

* No, I can't just wait for my slimes to reproduce. That would take too long and make the new slime pretty much useless for my purposes for too long. (The whole thing would take 2 weeks at best, 3 months at worst.) It's easier to just get an already close-to-neutral pH slime out of the wild, cycle water through it until it has gotten as clean as possible, and then change the newly made Aqueous Slime into whatever I need by feeding it appropriately. (At most, 1 month.) Otherwise, I use too much water cleaning the bred slimes. (At this point, though, I'm pretty sure a couple people from the Guild already have prepared "wild" slimes to sell to me because of this... but it's still unnecessary spending, though.) The slimes I breed are better off selling for money. (*Not to mention this Purple Paint Slime abomination...*)
* No, I can't just tame the slimes with food or toys to keep them here... They're too mindless. They eat what they find unless they get hungry. Only then do they hunt. Since they seemingly can't taste, they don't care if they get their food from me or elsewhere... Just wherever they end up hopping, sliding, and/or oozing across first. (Depends on the slime.)
* Slimes won't split to be smaller than $8π\,in^3$ OR $131π\,cm^3$
* A slime can slip through smaller cracks based on their kind. A paint slime can slip through the crack between a door and door frame, but the lamp oil slime can slide pretty much anywhere water can. Additionally, a sticky material allows slimes some climbing ability, so paint slimes can just crawl up walls if the ceiling is exposed. That said, while some can climb smooth, vertical surfaces, I do not at this time have any that can cling to the underside of smooth, horizontal surfaces.
* If two slimes meet, either one will eat the other (becoming contaminated and unusable, so imagine if lamp oil got mixed into your milk) or the two slimes will mix (creating abominations like the purple paint slime).
* Slimes need enough food or liquid to maintain their mass as they do excrete some of it regularly.
* Slimes do not need air to survive; however, the air available (and lack thereof in some cases) can influence a slime's *quality*. Some benefit from air. Some benefit from a lack of air. That said, air availability is less of a concern of mine.
* Slimes do not need more food or liquid than necessary to maintain their size, thus preventing agitation. That said, they do need specific material input based on what kind of slime they are to be. For example, I have to feed a Red Paint Slime appropriate Red Pigment for its paint. If I feed it liquid, I risk diluting it. If I feed it something else, I risk contaminating it. (Like that Purple Paint Slime disappointment is.) A Barbecue Slime is easier to maintain in that I can use a variety of ingredients, thus depleting my food stores for it more slowly, and can cheat on some ingredients temporarily.

While you already know, adventurers, here are some of the things not to forget about this world we live in:

* Skilled mages are limited to the point of being effectively nonexistent. The best I could ask a mage to do is cast an Ice spell constantly to keep the slimes in the enclosure, but the money it would take is impossible to accrue even if I sold the most valuable slimes I have. (Ignoring that one such gold mine ran away today it seems!) Beyond that, even the most talented of mages has enough mana to cast the spells necessary once ever few hours. In the summer, the ice would melt in minutes. Finding enough capable mages would be actually impossible. So, no requiring mages (or magical items), please.
* Craftsmen likewise aren't generally helpful. Back home, there was concrete I could use, but in this world nobody knows how to make it. It looks like the extent of materials available is wood, glass, stone, rudimentary metals, clay, and so forth. While a craftsman could probably make something, I'm concerned the cracks between pieces will still afford the slimes a chance to ooze out and escape. If your solution requires a craftsman, the fewer pieces and types of materials necessary the better.
* The world is very medieval in a lot of ways. Right, that won't mean anything to you... Basically, our technology is really limited. So don't suggest something that would require sophisticated technology. There was someone a town over who was burned for being a devil-worshiper because he came up with a highly rudimentary sewage system for his town. (He was reincarnated as a dragon, so it's fine now... but I was already dragged into this world from another. I don't want to risk reincarnation on top of that.)

So, basically, here is what you have to work with:

* I have plenty enough land available to me. (about 2.5 acres/10,000 m$^2$)
* I feed the slimes myself once a day so they don't get restless nor grow too out-of-hand in size. This means I need some kind of opening or slot that I can put their food into in order to keep them fed. At the same time, this means the slime could potentially escape that way, which I want to avoid.
* I need to be able to access the pen in order to get the products I'll need for the day. I do so by manually harvesting from them using a spoon, ladle, or even a cup or bowl (depending on how much I may need). (I have to keep these tools regularly cleaned lest I risk contaminating my Slimes.)
* They are semifluid, yes, but I can't just manually separate them by pouring them out. Their membrane will keep them held together. The only reason why I can scoop their internal fluid out is because I can exert more force than their membrane's surface tension does. Anything that isn't inside the vessel I am withdrawing, though, will be retained in the slime which is convenient for preventing resource-loss.
* My slimes are pretty docile unless I forget to feed them for too long. I have no intention of being away for a week, so it SHOULD be fine, but just in case, assume an agitated "large" slime has the physical strength of a medium-sized dog like a Border Collie. (Actually large slimes are worse, but I have no intention of letting mine get *that* big.)
* Their acidity is about equivalent to Lemon Juice at worst. I make sure to keep them from being too concentrated, but assume a Lemon Juice Slime is just as concentrated as the lemon juice bottles you can buy in a store. (I used to have one before it mixed with a Sugar Water Slime... and now I have a Lemonade Slime... best mistake I ever made.) I try to avoid having anything that's TOO dangerous, so no HCL or HF, but still, I do have Slimes that make food preparation so much easier.
* Their strength and acidity may not seem that bad on their own, but consider those factors together and the durability of any materials used.

The best answer is one that uses the fewest types of materials, the fewest number of fastened-together pieces, holds together well, and gives me the best access to my slimes while they still can't get out. Basically, the best while cheapest pen wins. I'll even pay 10 Silver Coins (100 Reputation) to the winner (once I can place a bounty on this)!

---

So, I am awarding the Bounty now. While there were quite a few answers that were all great in their own ways, I had to debate between the following to see which best fit my needs:

* Bundt Cake Pen (@Willk)
* Specially-Made Glass Jugs (@Kingledion)
* Pithos/Amphora (@Cyn)
* Barrel (@Tim B II)

(Honorable mention to @L. Dutch for the idea of using Lotus Leaves and their naturally hydrophobic qualities.)

This isn't to say that other ideas weren't good, they were, but these were the strongest ideas. That said, there can only be one winner. After careful consideration, I gave the Bounty to @Willk. This was a tough choice, but I think it was the right one as the size I would need @Kingledion's Jugs to be, I'd essentially just have a glass pithos/amphora, thus meaning I basically just used @Cyn's idea. The issue is, I'm not personally very strong, so removing and returning a bunch of heavy lids every day isn't going to work well for me, so I decided I would decide between @Willk's idea and @Tim B II's idea. Unfortunately, I had to consider @Tim B II's idea much like @Cyn's idea because of all that goes into removing a barrel head and putting it back on. In the end, I gave the Bounty to @Willk because his best fit my needs and my ability. Still, I appreciate everybody's input and I hope everyone had fun with coming up with ways to solve my issue. Technically, @Cyn, @Kingledion, and @Tim B II all had good ideas that work. The issue is simply with the fact I would be unable to make effective use of them. But who knows? Maybe somebody else could use their ideas for their own Slime Farms! :D

Come by the tavern I work at sometime. I'll treat everyone who contributed to a round of pancakes with Maple Syrup Slime Maple Syrup! It's the best syrup I've had since coming to this world! :D