Placing Catch Basins
A catch basin is a below-grade collection chamber that receives drainage from multiple inlets and routes the combined flow through a single outgoing pipe toward the outlet.
Catch BasinA catch basin is a below-grade collection chamber used where multiple drain pipes converge before continuing to an outlet. The Catch Basin object places a junction node on the plan that accepts incoming pipes and routes a single outgoing pipe to the outlet. In the Inspector you set a fixture style (Concrete Square, Round Riser, or Green Lid) and the Basin Depth (0.15–0.8 m). Use a catch basin wherever two or more drain inlets or pipe runs meet, or where the network needs a transition or maintenance access point.
Activate the Place Catch Basin tool
In Drainage mode, click the Place Catch Basin button in the toolbar. The cursor changes to a placement crosshair. Move the cursor to the intended location on the canvas.
Click to place the basin
Click on the canvas to place the catch basin. It appears as a square or rectangular symbol on the 2D plan. You can reposition it after placement by selecting it with the Select tool and dragging.
Configure dimensions and burial depth
Select the basin to open the Inspector. Set the plan dimensions (width and length in meters) to match the specified basin size. In the Burial Settings section, set the burial mode to Buried and enter the depth in millimeters. The depth should reflect the top of the basin lid relative to finished grade.
Connect incoming and outgoing pipes
Switch to the Draw Pipe tool. Draw pipes from each drain inlet to the catch basin — the pipe endpoints snap to the basin's connection points. Then draw a single outgoing pipe from the basin to the outlet point. This outgoing pipe typically has a larger diameter than the incoming pipes to handle the combined flow.
Connect incoming drain pipes
Place a Drain Pipe from the Conveyance & Discharge section. Draw each incoming pipe from its drain inlet (or previous pipe segment) to the catch basin node. Repeat for every incoming run that terminates at this basin.
Route the outgoing pipe to the outlet
Draw one Drain Pipe from the catch basin toward the outlet point. This single outgoing pipe carries the combined flow, so select it and set a diameter equal to or larger than the incoming runs. Connect the far end to an Outlet to complete the network.
Review the connected pipes
Select each connected pipe and confirm its diameter and burial settings in the Inspector. Record the basin's chamber size in the Name field or via a note for the construction documents.
Size the outgoing pipe to carry the combined flow of every incoming pipe. A common rule of thumb: if three 110 mm inlets feed one basin, the outgoing pipe should be at least 160–200 mm. Confirm sizing with a civil engineer or hydraulic calculation.
Catch basins and drain inlets serve different roles. A drain inlet collects surface water at one point and is visible at grade. A catch basin is a subsurface junction — it joins pipe runs below ground. Use inlets to collect water, then route their pipes into a catch basin before the outlet.
Frequently Asked Questions
How many pipes can connect to a single catch basin?
There is no enforced limit on how many pipes you can route to a catch basin node. Most site drainage designs use two to four incoming pipes per basin. For more than four, consider splitting them across two basins in series to keep the plan readable.
When should I use a catch basin instead of a drain inlet?
Use a drain inlet to collect surface runoff at a single visible point. Use a catch basin where multiple pipe runs join underground, or where the network transitions to a larger-diameter outgoing run. Inlets typically feed into basins, which then feed into the outlet.
Can I set the basin depth?
Yes. The Inspector's Basin section has a Basin Depth slider (0.15–0.8 m). Physical chamber dimensions beyond depth are not modeled parametrically — record them in the Name field or a note for the contractor.
Can I place a catch basin in the middle of an existing pipe run?
Yes. Place the basin at the midpoint, then split the existing pipe by deleting the segment and re-drawing two pipes — one from the upstream end to the basin and one from the basin to the downstream end.