You don't need to put anything on the caps of bottles to seal them. If you drill the holes small enough in the caps so you have to cut the hose at an angle and pull it through with a pair of pliers, in other words, Tight... then you will not have to seal them either.
Just make up a soap and water solution to check for leaks after it is up and running under pressure.
10 gallon hospital tank.
29 & 50 gallon - High Tech C02 enriched.
50 gallon Pond - Natural.