I just completed installation of new brass drain tubes on a 1988 Montauk.
After replacing the three-inch stern drain and three-inch anchor locker drain, I thought the 12-inch stern center drain would be straight forward, but due to compound angles at both ends it was not.
I bought 1-inch-OD 0.032-inch wall brass tubing from McMaster Carr in three-foot length.
I used a flaring tool. I bought a 36-inch length 5/16-inch threaded rod to allow the flaring tool to have an extended reach.
I had some hardwood wedges with about a 10 to 15-degree angle to tilt the flaring tool die as I formed the flares.
I started by using the removed drain tube as a template.
I cut an approximately 15-degree angle in one end of the new drain tube.
I annealed the brass and formed the inboard end first.
I realized that the factory installed tube had a slight bend near the end, so I annealed a couple inches of the tube back from the flare and checked fitment: it was a very close match to fiberglass inside the hull drain area.
I made a slight bend downward; this improved the flanged angle matchup to the fiberglass.
I then inserted the new drain tube with an O-ring installed. I took a measurement on the outboard tube flange area with two O-rings installed; I added an extra 1/16-inch beyond the second O-ring.
The outboard end of the tube was also cut at an angle, maybe 5-degrees.
After making the cut, the outboard of the tube was annealed.
I then put together the assembly using 3M4200. (Note that 3M5200 is too strong and would make removal of the tube very hard.)
I used a wood wedge inside the boat laid against the previously formed flare beyond the threaded rod, down the drain, and connected the outer flare die to the rod.
I put [lubricant] on the die to aid in smooth rolling.
I double nutted the rod inside the boat and tightened [the nut on the outboard end of the threaded rod], thus flaring the outboard end of the new drain tube.
While flaring I noticed the [inboard end of the tube] O-ring had started to squeeze out a bit.
I then stopped [tightening the nut on outboard end of the threaded rod]. I used a ball-peen hammer to reshape [the inboard end of the drain tube], pushing O-ring back under the rolled edge of the drain tube. The flare rolled edge was tapped lightly so it re-captured the O-ring. I held a trailer hitch ball against the outboard end of the new drain tube while tapping lightly.
Thanks to the use of annealing, I was surprised at how easily I could tap the brass tube surfaces into perfect final form. The metal is soft.
I cleaned up the 3M4200 sealant.
I gave a few small taps to alter the final shape of the drain tube rolled end flares.
The outcome looks [as good as the original installation at the] factory.
I hope this helps someone [to install new brass drain tubes].
--Pat
Brass Drain Tube Installation Detailed Procedure and Hints
Re: Brass Drain Tube Installation Detailed Procedure and Hints
Great detailed report, good luck, I know it was not straight forward. I was surprised My 2006 dauntless had plastic thru hulls. I replaced them in the Fall, just hope what I did doesn't leak, I had to make a press to pull the tubes together and I sealed with a caulk BW recommended instead of the 4200 or 5200.