There are only a few glues available that will bond polyethylene to other plastics permanently.
Tap Plastics makes one
as well as this product
from 3M. If you use one of these adhesives, it will be permanent.
Another way that works for me-
Insert a length of 1.5" ABS pipe into the outlet and seal it with adhesive sealant and a stainless steel hose clamp. Clean the tank outlet with a strong solvent such as MEK or acetone, then coat the part of the ABS pipe that will insert into the tank outlet with a high quality polyurethane ADHESIVE/sealant like 3M 560 or 3M 5200 fast cure. Secure with a hose clamp and allow the sealant to completely cure before leak testing.
Good luck on your project!