All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
This religion is a religion of tolerance and Mercy, praise be to Allah.
Allah relieved us from having any burdens or hardships in religion. However, it is people who make things difficult for themselves because of exaggeration and giving in to whispers.
If you avoid exaggeration and whispers, your life will become easy and all your matters will be as good as they were before and even better.
Hence, do not stay long in the toilet; rather, as soon as you have relieved yourself, perform Istinjaa' (cleansing yourself). It is sufficient for you to predominantly believe that you have purified yourself and it is not a condition to be absolutely certain about that.
Therefore, once you predominantly believe that you have achieved purity, then get up straight away and do not pay attention to any whispers that you might have afterwards.
No matter how much the devil whispers to you that you discharged urine after that, do not take this into consideration, and do not smell or investigate whether or not you have discharged anything.
In case you find the trace of wetness and it is probable that it is the remaining water of Istinjaa', then you should assume that it is. Moreover, do not assume that you have discharged anything unless you are certain; a certainty upon which you can swear.
If you follow these steps, then you will not have any problem at all -Allah willing.
For more benefit on Istinjaa', please refer to Fataawa 364612, 343681 and 271426.
Allah knows best.