It's just barely possible that at least part of the solution to your problem MIGHT be in putting the loop in another location. Are we talking about the intake vented loop or a loop in the head discharge line? If the intake, where are you trying to install it--a) in the line between the thru-hull and the pump or...b) between the pump and the bowl?
Warming the hose (I've always preferred a blow dryer to lugging pots of hot water
from the galley
to wherever the hose connection is), being careful not to over heat it, and lubing both the hose barb and the inside of the hose with dish washing
liquid---or better yet, K-Y--should allow you to slip the hose well onto the barb...then double clamp, with screws 180 degrees apart.