I have not done this on the Cruiser, but on my last unit, I installed a CPVC ball valve and it did not limit the flow as much as a brass petcock. But in either case, there is a lot of water at the bottom of the tank which doesn't get drained even when the nylon drain plug is removed. You can get more stale water and sediment out of the tank with a wet/dry vac and a small diameter plastic hose.
Texas Baptist Men-Retiree Builders member since '01
13 Silverado 3500HD D/A, 2wd CCSB srw, custom RKI bed
11 Cruiser CF32MK