Tee manholes obtained by means of a rotational moulding process contain three sockets for the inlet and outlet of the corrugated pipes and always include a corrugated pipe for the riser.
This solution is usually adopted in Italy for road and motorway works for the construction of manholes to connect corrugated polyethylene pipes.
Tee manholes have a socket at the upper part capable of accommodating an extension consisting of an Ecopal corrugated pipe of the same diameter. Risers of 600 mm may be reduced for the manhole crawl space, and pipes with differing inlet and outlet diameters are available.
Ends of manholes with ND/OD 800 – 1000 – 1200 risers can be created using a PEMD conical reduction adaptor, obtained by rotomoulding and coupled onto the extension, which is used to reduce manholes up to a crawl space diameter of 600 mm.
A ladder, consisting of polyethylene uprights and polyethylene-coated steel steps, may also be welded onto the inside wall of ND/OD 1000 – 1200 risers.