On Oct 8, 10:07 am, MNRebecca wrote:
Tried to walk the dog between storms yesterday and got caught in a
downpour which yielded unexpected results. I saw something I might
otherwise never have known about. When the rain comes down really
hard, water backs up out of a downspout elbow, shooting into the air
like a fountain (to land in a vulnerable, leak-inducing area) instead
of continuing along the long, extended horizontal downspout track* to
drain away from the house/foundation. Before I look into wider
downspouts and elbows, I'd like to try sealing thoroughly. What will
work better, duct tape or gutter sealant?

*Downspout runs the length of the house, about 40 feet (with one
additional 90 degree turn besides the elbow) before spilling onto the
lawn to run down a hill. This was necessary as the neighbor's
property, just a few feet away, slopes down towards my house. No room
to effectively release water without navigating the length of the
house.

R-

You don't have a sealing problem, you have a "blockage problem".
Forty feet of "downspout", really drain line, and two elbows are
probably a little excessive...so the water is backing up &
pressurizing the joint that you see spraying water. You could (when
its dry) seal the joint wiht aluminum tape but that's only fixing the
symptom. You need to make sure your the drainline portion of your run
is free of obstruction & when clean, it is able to handle the
necessary flow.

If cleaning (bust open the joint & blast the drainline clean with a
hose) fixes the problem, you're done. If not consider replacing the
drainline portion of the "downspout" system with a 3" or 4" plastic
drainline. Dump the real downspout into the new drainline. Ideally
you'll need ~10" of drop for the drainline....if you have less, this
might be the cause of the backup.

If you go with the drainline fix, use a sweep T fitting with a
cleanout to make maint easier.

cheers
Bob