@Jereme asked about this.
Here is Venerable Ru De talking about this topic (Starting from the 1min 50s mark):
若有法寶如佛像、經書、唐卡、等，因為汙損或其他原因，不得已，必須銷毀，為恭敬故，欲焚毀前，可唸以下之咒語及偈子，並觀想佛菩薩自佛像中離開回到佛國土去。
I think the crux is to respectfully do the action and visualise the Buddhas and Bodhisattvas going back to their realm
咒語：唵 班紮 北 嘎 (瑪) 啊 札 瑪 吽 (共9或10字 可唸3遍或7遍或21遍)
偈子：尊已成辦眾生利，賜予相順諸悉地；現雖已至佛境地，祈願再度降來臨。(或唸白話如下：您成辦一切有情事業、並賜予相同之成就、雖然現在到佛的境地、祈求您能再降臨此處)
And then reciting the above mantra.
This topic was re-visited by Venerable Ru Jun in a recent Q&A online discourse I attended.
Some pointers shared by fellow attendees:
When disposing the Buddhist objects or going into dirty places (e.g. toilets) with scriptures/relics, we can recite the 金剛力咒 in one of the following ways:
佛法字紙、佛像、唐卡處理方式 【金剛力咒】兩種參考版本如下：
1.唵 班紮 北 嘎瑪 阿扎嗎 吽
2.唵 班紮 北 嘎 阿扎嗎 吽
尊已成辦眾生利 賜予相順諸悉地 現雖已至佛境地 祈願再度降來臨
or
尊已成辦眾生利 賜予相順諸悉地 現雖已至佛境地 祈願再度降來臨 唵 班雜 貝嘎瑪阿雜瑪 吽 [三遍]
咒持唸三次
I also found another video with Venerable Ru De doing some explanation on this.
