Can electrical solder be used for joining pipe?
My understanding is that plumbing flux is more aggressive (acidic) and will damage electronics, but that you can go the other way and use flux-core solder on plumbing in a pinch. A few caveats:

Electrical solder is often a softer alloy, so it won't withstand pressure as well.
Definitely flux the pipe fittings as you normally would. You won't get good coverage with the flux in the solder.
You may struggle to get enough material in the joint in a timely manner. Plumbing solder is about 5 times the diameter, meaning about 20 times the volume. You might fold the electrical solder back on itself several times and give it a twist in preparation for quicker flow.
Wipe away any leftover flux after the joint cools. It can be corrosive.