Ice machine drains mostly clog from slime in the bin drain and from lines that sag, run too small or lack a vent. Dish machine drains collect food solids and hard-water scale in the receptor and short run to the floor sink. Keep the air gap, clean on the maker's schedule, and shut off water if it overflows.
Ice machine drains
Hoshizaki's installation manual for its AM-50 series warns that "slime may build up inside the ice storage bin drain and prevent water from draining properly," and says to clean it "once every 3 months or as often as necessary for conditions." Its warning is plain: "If the ice storage bin drain becomes clogged, water could build up in the bin and overflow." A bin that holds water instead of draining usually has slime or debris in the drain.
The installation matters just as much. The manual says "Drain line should not be piped directly to the sewer system," calls for an air gap of at least 2 vertical inches, a fall of 1/4 inch per foot on horizontal runs for gravity drains and a vented tee connection. A drain that sags, is too small or has a trap with no vent drains poorly, so it clogs and overflows sooner. Maricopa County's guide asks for a minimum 1-inch air gap on indirect waste lines, so where both apply meet the larger gap. How to drain a commercial ice machine legally has the rules, and gravity versus pumped drains covers pump failures.
Phoenix's FOG manual also says "Condensate or cooler drain lines shall not be routed to the MS/GW line," so ice and cooler drains belong on their own receptor, not the grease-bearing line.
Dish machine drains
A dish machine empties into a floor sink or trapped receptor through a short indirect line. Food solids and scale collect in that receptor. Maricopa's guide notes that "Due to the presence of hard water in Maricopa County, it is recommended that a quality water softener or filter be installed to reduce problems typically associated with hard water, such as limescale and mineral buildup," and names drain lines, dishwashers and ice machines. If the receptor spills only when the machine dumps, see why the floor sink backs up when the dish machine runs.
If it is overflowing now
For an ice machine, Hoshizaki's instruction is: "If water collects in the bin and will not drain, turn off the icemaker and close the water supply line shut-off valve. Call for service." For a dish machine, stop the cycle and keep wastewater from reaching food areas. Then have the drain cleared and the line checked for slope and the air gap.
A clean receptor, a free-draining bin and an intact air gap are the three things to keep. If the drain clogs again soon after clearing, the line behind the receptor needs jetting and a camera. We handle that on a schedule that works around service hours, with the price quoted up front.