What no -toxic sealant to use on the RO container

[TAHK]

I am in the process of assembling RO system and am using the 55 gal barrel for the storage. I had to put the float switches in. There are rubber gaskets that I have put on the inside of the barrel as per assembly instructions. However, the bottom switch leaks. I am quite sure I have not overtightened the gasket and also quite sure that the hole is drilled to manufacturer specifications 3/8 in. Do you folks have any suggestions regarding the sealant for such situation?
I truly appreciate the advice.

 

[Mical]

silcone

 

[LRT]

I use reef aquarium silicone for all my fittings and connections and havent had a leak yet.

 

[TAHK]

Thank you! I’ll try silicone.