Just think of the missed opportunity. You could shower without using water from your tank! That's called sustainable living. Or something.
John, K3NOQ, is right. If you didn't stop-drill at the very end of the existing crack to relieve the stress concentration, you should go back up there and do so, else the crack will certainly grow when the plastic heats in daytime and cools at night. A 1/16 or 1/8 drill is about right.
__________________
-- Carl
|