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Are your old ones thrashed?

Not sure on a Montauk, transom drains on my Outrage I use 3" x 1 1/4 dia. and cut them to length and flare..Thru hull drains are 1'' dia.

You can get away with a 3" and cut them to length.

Pull your old tubes out - put a new tube in, one end flared w/ or without Orings (you can buy them with one end flared), your call..
Mark it on the other end about an 1/8 (or more if using Orings) from opening, to allow for the flare and cut the tube with a good pipe cutter.the little hand held cutters work great

Some say to heat the ends before flaring..I never have - your call.

Use your flaring tool and two socket wrenches, some 4200 and your good.