1 Large TAP will drain in 1 hr - 1/12
6 Large TAP will drain in 1 hr - 6/12 i.e. 1/2
1 Small TAP will drain in 1 hr - 1/18
6 Small TAP will drain in 1 hr - 6/18 i.e. 1/3
So 6 Large and 6 Small Tap will drain in 1 Hr - 5/6
Total Drain time - 6/5 i.e. 1 Hr 12 Minute