Xaiv lub npog manhole zoo li yuav khau; qhov zoo haum yog qhov tseem ceeb tshaj plaws:
Rau qhov chaw ntub dej, ua qhov tseem ceeb ntawm xeb- cov ntaub ntawv tiv taus.
Tso cai rau 20% qhov hnyav pub rau kev tsav tsheb.
Rau cov siv tawv ntsuab, xav txog ib qho kev tsim perforated los txhawb cov kua dej.
Ntsuas lub taub sab hauv thiab sab nraud ntawm qhov qhib qhov manhole ua ntej kev teeb tsa.
