Does code allow flexible PVC for drain through joists?
Flexible drain lines are VERY prone to &quot;double-trapping&quot; themselves and failing to work. I don't know from a code POV but I'd guess not, and I know from experience that &quot;draining things with hoses&quot; can be fraught with peril - yes, I note that you said carefully supported.
In most cases by using slightly oversized holes and exploiting the slight flex of &quot;rigid&quot; pvc it is possible to get &quot;longer than one joist bay&quot; sections of pipe between joists. You can almost always get a two-joist bay section (i.e. 32&quot; in this case) section in place just by angling it up and then rotating. Whether you can get more than that depends on the size of the pipe and the position of the holes relative to the bottom of the joists, unless you can get &quot;end access&quot; at one end to stick it in straight.
The other option is to run it below the joists.