450 x600 concrete manhole sections, pipe enters one side, silt drops to the bottom pipe exits other side.
concrete sections are about £40 and a lid about the same, so you have £200 in materials with the concrete base to sit it all on, then your labour to core drill two 110mm holes.
the choice is yours, all these things are designed to cut down on labour, so £25-£30 an hour for 4 hours to fit it.