Pouches often have a little leakage and yet work just fine.  Make
sure you are testing them with the bleeds blocked off with your finger.
I use thinned rubber cement followed with talcum powder or baby powder.
Some guys thin PVC-E with a little water and use that sparingly --
a little goes a long way.  Anything else is really not correct.

By the way, you can seal your pump leather if you cover your pump in
leather.

Don Teach
Shreveport, Louisiana