Here are some results of that rule:
4-letter words
bout, gout, lout, pout, rout, tout
5-letter words
about, clout, flout, glout, grout, knout, scout, shout, snout, spout, stout, trout
6-letter words
buyout, cutout, devout, dimout, dugout, layout, mahout, payout, pigout, putout, ragout, redout, rubout, runout, setout, sprout, tryout
7-letter words
backout, bailout, beshout, blowout, burgout, burnout, cookout, dropout, eelpout, fallout, foldout, grayout, handout, hangout, hideout, holdout, lockout, lookout, missout, pullout, rainout, readout, rollout, sellout, shutout, sickout, slipout, spinout, surtout, takeout, timeout, turnout, walkout, washout, wipeout, without, workout
8-letter words
blackout, breakout, brownout, bullpout, carryout, checkout, closeout, flameout, freakout, gadabout, hornpout, indevout, knockout, layabout, marabout, phaseout, pitchout, printout, resprout, runabout, seascout, shakeout, shootout, stakeout, standout, stickout, undevout, watchout, whiteout
9-letter words
dishclout, downspout, groundout, hereabout, rainspout, stirabout, strikeout, turnabout, walkabout
10-letter words
knockabout, roundabout, rouseabout, roustabout, superscout, thereabout, throughout, waterspout, whereabout
11-letter words
breechclout