Hello all. A while ago I made a hive top feeder but for the life of me could not get it to stop leaking. I tried wax (bee and paraffin). I tried silicone and something made for boats that was suggested to me. Nothing kept it from leaking. So they got put into a corner. I recently had a small leak in my roof around a vent and used this stuff called flex seal, which is essentially liquid rubber in a spray can. It was very easy to use and it made me wonder why I couldn't spray it in my feeders. I figured I'd better ask first before using something like that in my feeder. I would likely spray now and use in the spring so it would have plenty of time to sit.
Once you've applied wax to a joint you want to make waterproof, you've pretty-much knackered it with regard to the use of any other sealant, as wax is commonly used as a release agent - i.e. to prevent glues/adhesives from sticking to a surface.
LJ
I can't comment about the effect of the rubber on the feed/bees.
However the FlexSeal wouldn't need to adhere well to the inside (ie bottom and corners) of your feeder. As long as it was thick enough to be water tight and adhered well enough near the top of the feeder so that the sides didn't flop down and allow syrup to spill over the side.
Line the feeder with a plastic bag.
If it is wood, then abby warres old book was an avocate of enough coats of paint to fill the cracks. I have made two feeders and I just painted the inside. They don't seem to leak (YET).
Good luck
gww