Except I truly don't put my finger in holes I drill that don't go where I know. I too think pressure switch. I pulled my belt driven pump. Put in new shur-flo and have much better pressure with no pressure switch.
Hole in tank I fixz with epoxy where applicable until I can replace. I found my drain valve for water tank under the arm of couch, pulled arms up, (straight up), and found valve and air breaker line to water tank. Drainage is a relatively slow process as it is a 1/2 " line and drains about 25 gallons (My estimate from size of tank)