Really large PVC

[Cooler]

You really want to look under "plastic drainage pvc pipe".

Big enough?

[blackhat]

I would go with the largest rectangular opening I had and line it with surface tempered hardboard. Actually I would line it with sheet metal duct but I have fabrication facilities I could make my own.

[Scouter]

I looked at HD and Lowes, really odd. They have duct stack that, depth wise, is a perfect fit at 3-1/2", it comes in widths of 10", 12" and 14". Only the 10" has a 45-deg elbow. Because of where the duct would empty out in the laundry room I have to put an elbow and a 3' run into the catch basket. Most of the project sites I've read recommend 12" or 14" to lower the chance of laundry getting caught in the elbow.

[JosephP]

I looked at HD and Lowes, really odd. They have duct stack that, depth wise, is a perfect fit at 3-1/2", it comes in widths of 10", 12" and 14". Only the 10" has a 45-deg elbow. Because of where the duct would empty out in the laundry room I have to put an elbow and a 3' run into the catch basket. Most of the project sites I've read recommend 12" or 14" to lower the chance of laundry getting caught in the elbow.

Call a local HVAC shop.  Many fabricate their own and it wouldn't be that expensive for them to make you an elbow.

[Anak]

Call a local HVAC shop.  Many fabricate their own and it wouldn't be that expensive for them to make you an elbow.

And if they don't fabricate their own, find out who does their sheet metal work for them.

I have found a local guy who is very reasonable. 

Pay a bit extra on the material side and you can have it in stainless steel.

[TDKPE]

Any tin knocker can make a rectangular elbow of any size, shape, and radius you want in less time than it takes to describe it.  It's what they do.  

[Scouter]

Thanks. Will see if I can find a local sheet metal worker.

[Bob10]

Thanks. Will see if I can find a local sheet metal worker.

I couple of clamps, snips and some 2 x 4 can turn you into a sheet metal worker.  Wear gloves or stock up on bandages.

Rivets or self tapping screws from the inside out to avoid snagging stuff

[chrisntam]

Here's what I recommend:

[daddo]

I'd use the hardboard or fiberglass sheets.