19mm Top Hat Grommets are the ideal way to create a water tight seal on an un-drilled reservoir.

Simply drill a 23mm hole at the bottom of the container you intend to use as a reservoir.

Insert the 19mm Top Hat Grommet into the resulting hole.

Then pass your 19mm pipe in through the grommet. This will form a water tight connection.

Ideally an inline tap and inline filter should be inserted into the pipework outside your reservoir.