W=18"   L=35"   D=9"   B=9"      15 gallon tank. 

Use a hole saw to create holes for ABS fitting.  For 3" fitting use a 3 1/8" hole saw.  For 2" fitting use a 2 1/8" hole saw.  For 1 1/2" fitting use a 1 5/8" hole saw.  Use ABS cement to install fittings.  Repairs can be made with ABS cement.  MFG# HT 147