A drain hole can empty the finished part and still arrive too late to help during printing. Inspect the cavity twice: once in layer order, to see when it first opens, and once in the orientation you will use to drain and wash it. A hole hidden under the base of a figurine can pass one check and fail the other.
Follow the cavity as it forms
Imagine a hollow bust with a flat base and a partition inside the shoulders. A hole through the base may reach the chest while leaving the head sealed. In the slicer, hide the outer surface or use a clipping plane. Trace a path from each pocket to the outside. Then step through the layers from the build platform onward. Find the first layer where the shell encloses an area and the first where that pocket communicates with the outside. A cavity that stays closed between those two layers deserves another look. Formlabs illustrates how orientation creates a suction cup in bottom-up printing. PreForm cup detection
| What the preview shows | What to change before printing |
|---|---|
| The chest drains, but the head is a separate closed pocket | Open a path from that pocket or leave that region solid. |
| The opening appears only after a long run of cupped layers | Move an opening toward the first layers of the cavity, or change the orientation and inspect it again. |
| A hole is visible from outside but stops inside the wall | Extend it through the shell. Inspect its cross-section after slicing. |
| Resin can drain in one position, but there is no clear path for air or wash fluid | Plan another accessible opening and check it in the washing orientation. |
Choose a hole you can actually use
PrusaSlicer lets you set both depth and diameter and preview the hollowed mesh. Prusa recommends at least two drainage holes. On a divided model, counting openings across the whole object can mislead: both may lead to the same compartment. Formlabs also recommends drainage holes when hollowing and distinguishes trapped material from suction during the build. Neither workflow yields a single hole diameter for every shell. PrusaSlicer hollowing · PreForm hollowing
For a small solid detail with no practical wash access, compare the solid and hollow versions in preview. The resin you would save is visible in the slicer estimate. The internal pocket you would have to clean is visible in the section view. That comparison is a better basis for a decision than hollowing the entire model by default. For the subsequent cleaning step, check the part dimensions against the wash station’s usable space .
Handle uncured resin and contaminated wash liquid according to the resin’s safety data sheet. A hole that stops dripping does not establish that its interior is clean or cured. Formlabs resin care