Super-soaker (the brand-name version) is decent for sealing. I used to carry several around in my car trunk in the summer for impromptu water fights with the neighborhood children.

As an added bonus if you feel like pulling out a Kitty Tactical Nuke for those supreme corrective moments, they have some that'll spew 1.8 litres of water in 5 seconds flat.

Cleanup indoors may not be worth this, however, so they do offer smaller models.