Squeaky Clean Sprint

Squeaky Clean Sprint is a course featured in Wave 5 of the Booster Course Pass for Mario Kart 8 Deluxe as the fourth and last course of the Feather Cup. The course is set in a giant bathroom, similarly to how is set in a giant bedroom. The course takes racers through various departments within the bathroom, such as counters, shelves, bathtubs, and drains. According to internal data, this course was created as a new course for Mario Kart Tour, despite being revealed for Mario Kart 8 Deluxe first, similar to Sky-High Sundae and Yoshi's Island.

Throughout the course are various items commonly found in a bathroom. The starting banner is held up by two cups, each containing scissors, toothpaste, a toothbrush, and a hairbrush, while two balloons hold up another banner. Various bottles of hair mousse, shampoo, soap, and other fluids are seen throughout the course labelled with brands referencing various characters, one of which being labelled Toad Barber, a pun on Toad Harbor. Other objects seen throughout the course include sponges, hula hoops, inflatable balls, bars of soap, a fan, and sunglasses.

Excluding courses announced simultaneously, this course and Rome Avanti mark the shortest period of time between the announcement of two new courses for the Mario Kart series, with only a 16-hour gap; beating the previous courses with this distinction, Piranha Plant Cove and Yoshi's Island, by five days. It also debuts just five hours before Piranha Plant Pipeline debuts in Mario Kart Tour, which is the shortest period of time between the debuts of two courses for the Mario Kart series, excluding courses that debut together.

Course layout
The starting line is located directly next to a sink full of water. The racers pass through the sink before being taken to a fork in the road leading into a bathtub containing a hula hoop. Racers can choose to drive along sponges that lead them into the water, or they can take a ramp to go directly into the tub. After swerving around bath bombs, racers soon drive down the drain. Here, a wedding ring acts as an arch representing an off-road shortcut. After leaving the drain section, racers are along on the floor, avoiding soap next to a large fan. A half-pipe is located along the left turn afterwards. Racers then take a Glide Ramp over a toilet, which leads to one of two possible paths. The path on the bottom is made of towels and leads to the finish line. The upper path takes place along a wooden shelf which has a Glide Ramp at the end that takes players over an alternate finish line that hovers over the regular one. There is also the option to drive along the railing next to the sink, which contains some item boxes and a Dash Panel. Should this path be taken, a Mushroom Trampoline will lead players back to the bathtub.

References to the Super Mario franchise
Similarly to, the course contains a number of small references to various games from the Super Mario franchise in the background of the course:
 * A clock resembling a Para-Biddybud (and by extension a Biddybuggy) appears near the starting line.
 * A can of Princess Orange can be seen near the bathtub segment.
 * Stars pattern the bath curtains.
 * The tiled walls of the bathroom, seen most clearly around the bathtub, features the cloud sprite from Super Mario Bros.. The color, too, makes the wallpaper resemble the sky from World 1-1.
 * Lakitu's Cloud can be seen on several balloons.
 * There are several Blooper-shaped decorations in the washroom.
 * The supports on the wall beside the mirror resemble Warp Pipes. The mirror itself is in the shape of a Mushroom.
 * Sunglasses resembling those Princess Peach wears while visiting the Lake Kingdom in Super Mario Odyssey can be seen leaning on top of a suitcase.
 * The aforementioned suitcase has a number of stickers plastered on its side. These stickers depict, a Dolphin, a Shine Sprite advertisement for Sunshine Airport, and various sponsors also present elsewhere in the game.
 * There are some bottles on the counter that are colored green with lighter stripes, making them vaguely resemble the hills that appear in the backgrounds of grassland stages from multiple Mario games.
 * There is a bag on the counter labelled "Dino Dino Outdoor & Camping Goods", a reference to Dino Dino Jungle from Mario Kart: Double Dash!!.
 * There is a soap bottle modeled after a Yoshi's Egg on the counter near the starting line.
 * The ring found in the drain section of the track strongly resembles the Binding Band from Super Mario Odyssey.
 * The bars of soap littered around the course have various symbols carved into their sides including Mushrooms and Fire Flowers.