(1)、設she計ji問wen題ti。開kai發fa商shang對dui小xiao型xing住zhu宅zhai區qu的de室shi外wai管guan線xian設she計ji不bu重zhong視shi，一yi般ban待dai住zhu宅zhai樓lou接jie近jin竣jun工gong時shi，才cai進jin行xing室shi外wai管guan線xian的de設she計ji。這zhe時shi住zhu宅zhai樓lou的de排pai水shui出chu戶hu管guan已yi經jing定ding位wei，設she計ji者zhe隻zhi能neng以yi始shi端duan排pai水shui出chu戶hu管guan的de管guan底di標biao高gao和he市shi政zheng幹gan管guan接jie納na處chu管guan底di標biao高gao的de落luo差cha來lai計ji算suan坡po降jiang，十shi分fen被bei動dong。如ru果guo落luo差cha較jiao小xiao
，就jiu將jiang排pai水shui坡po度du降jiang至zhi小xiao
，甚shen至zhi加jia大da管guan徑jing以yi減jian小xiao坡po度du

，致zhi使shi出chu現xian排pai水shui流liu速su小xiao於yu自zi淨jing流liu速su
，汙wu物wu沉chen積ji造zao成cheng排pai汙wu不bu暢chang。排pai水shui出chu戶hu管guan口kou與yu室shi外wai窨xun井jing出chu汙wu口kou管guan底di平ping接jie，大da股gu水shui衝chong下xia時shi
，汙wu水shui首shou先xian從cong排pai水shui出chu戶hu管guan口kou衝chong出chu
，然ran後hou再zai回hui灌guan，降jiang低di流liu速su汙wu物wu沉chen積ji。進jin汙wu口kou悶men入ru汙wu水shui中zhong，不bu利li於yu疏shu通tong清qing理li。當dang內nei外wai落luo差cha過guo小xiao時shi，因yin受shou基ji礎chu梁liang的de限xian製zhi，為wei增zeng加jia始shi端duan部bu分fen排pai水shui出chu戶hu管guan的de標biao高gao
，隻zhi得de從cong梁liang的de頂ding部bu穿chuan過guo，再zai向xiang下xia經jing兩liang個ge90。彎頭進入室外窨井，會增加堵塞的機率和疏通難度。