I'm planning on installing an exhaust fan in my bathroom and I have a question about venting the air out of the house. I have read that normally you would vent the exhaust up and out the roof or sideways out the side of the house or soffit. Due to the location of the bathroom and set-up of the house I would have to vent the exhaust down then sideways and out the side of the house. Is there any problem with doing it this way? I have not been able to find any information talking about it.

The goal is to get the warm, moist air outside the building and from what you say this should work. Some installers and builder run the vents to the attic or to the soffits and this is just very bad workmanship. Venting a bath to the soffit, which is designed to allow air into the attic, just pulls moisture inside.

I agree with ballengerb1 100% get it to the outside if you can. Most clothes dryers vent down and then horizontal and work great so why not a bathroom exhaust.

Just be careful. Water may collect at the lowest point. Say you ran galvanized pipe up, across, down and out. Water could seep out of the elbow into places you don't want it to be.
Also make sure the one way doors are used to keep critters out and air from outside, outside.

I'm installing a Dundas.Jafine soffit exhaust vent in the soffit of my house. With the hole cut in the soffit and access to the attic opened, I only have a 3" opening in order to get past the framing at the edge of the roof (inside the attic). Is there a flexible or collapsible venting that can be compressed to get through the 3" space available then expand back to 4" to the exhaust fan?
I can't do anything right now so the attic is open, the holes are cut but installation has come to a standstill. Any suggestions? Would appreciate any help you'd care to offer. Thanks.

3" space is kinda undefined. 3" x 16", 3" dia, whatever.

Suggestion:

Get something custom made. Try to keep the cross-sectional area the same.

or Maybe 3" flex PVC will work?

Product Listing Flex PVC By The Foot White

Lots of details or pics are missing.