In case of Foreign Railways discharge treatment is different. Have seen the treatment in case of China - Tibet rail line shown in Nat Geo. They said that all Coaches have a discharge box underneath and this is where the discharges are stored. Once the train halts at a major station (usually every 6-8 hrs or so) where halt is 10 mins, a special teams awaits. The discharge is pumped out from the carriage to the trucks waiting (by use of pipes). The trucks ten take it to the treatment plant / sewage plant etc. The entire pumping process takes 10 mins max as they ensure everything is ready when the train arrives.
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They have also given the reason stating that if it is discharged enroute they will have to...
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incur additional costs as lyf of the rail track and sleepers decreases.
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I have for a longtym felt that such discharge system should be used in Indian Railways also.

The case is similar in England, Wales and Scotland [bit.ly/AqSBwl] ;
In England and Wales, the Environmental Permitting (England and Wales) Regulations 2010 (Schedule 3, D2) provide a special exemption to rail companies from the need to obtain a permit to dispose of this waste onto tracks. Similar exemptions are available in Scotland and Northern Ireland under their Waste Management Licensing regimes. This waste is deemed to be
low-risk waste that the Government has determined requires only light touch regulation.
The Rail companies must register the exercise of the exemption with the Environment Agency in England and Wales and in the case of Scotland and Northern Ireland registration is with the Scottish Environment Protection Agency (SEPA) and the Northern Ireland Environment...
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Agency (NIEA) respectively. Rail companies must also ensure that the quantity of waste deposited per discharge must not exceed 25 litres, however there is no cumulative limit and therefore tens of thousands of litres of sink and toilet waste are discharged onto Britain's railway tracks every year.
"Most newer train carriages contain effluent retention tanks that are emptied regularly at maintenance depots, however older carriages including those of the InterCity model 125 still discharge waste onto tracks. Rail operators have argued that a comprehensive retrofitting of the older stock would be disproportionate to any health risks and prohibitively expensive. Prompted by health and safety concerns, research carried out by the Rail Safety and Standards Board in 2004 concluded that the health risks to rail workers were considered low and normal hygienic practices could mitigate risks of any exposure to microbiological contamination.This affects a minority of trains in service today as toilets that flush onto the track are being phased out as new rolling stock is introduced.” However, it is possible that a significant percentage of the carriages that still discharge waste onto tracks may be in service for up to a further ten years. This would continue to impact routes across the country, a consideration the Commission is likely to take into account in any investigation.