Plastic manholes (aka access, inspection chambers)

[Malc]

Hi,

I need to reroute some drains doing away with a traditional manhole. Options for the new manhole are traditional 450x600 or plastic 315 diameter. Depth would ~0.5m. What's the consensus of opinion on small manholes (or more correctly access or inspection chambers). Are they ok to rod or am I going to wish I had an old style chamber if it ever blocks?

BTW I can't go for a 450 plastic as I need a level invert, well maybe a 5 might do with a 45 each end and only using 3. The 315 seems a better fit, main channel long 45 bend to kitchen sink etc., 45deg entry, gully (not a lot of use), 90 deg entry, stack. I'm also not sure if I can raise the invert level of kitchen sink pipe which I'd have to for a 450 and they aren't level inverts.

 

[Hugh Jaleak]

You'll struggle to get rods in a small chamber, but they're permitted for invert depths of up to 600mm so should be ok for your needs. If drains are laid properly then they should rarely, (if ever), block. Worst case scenario and they do bung up, and rods wont get round, then a jetting hose will. It'll just cost you more.